Supermassive Black Holes May Be Even Bigger Than Scientists Imagined

Scientists working with the Chandra X-Ray Observatory have determined that the biggest black holes in the universe might be even bigger than previously thought.

At this point, it's clear to most astronomers that lying at the center of nearly every galaxy is a supermassive black hole - black holes that have masses ranging from a few million to a few billion times the mass of the Sun. Elsewhere in the universe, astronomers have identified rare ultramassive black holes - black holes with masses 10 to 40 billion times that of the Sun. However, new findings from the Chandra X-Ray Observatory have demonstrated that ultramassive black holes may not be that rare after all - because many supermassive black holes are bigger than previously thought.

"These results may mean we don't really understand how the very biggest black holes coexist with their host galaxies," said co-author Andrew Fabian in a press release. "It looks like the behavior of these huge black holes has to differ from that of their less massive cousins in an important way."

The issue here comes from the way that astronomers determine the mass of black holes. Black hole masses have typically been determined in far away galaxies by using the correlation between how much infrared radiation is coming from the gasses spinning from the black hole and its mass by relying on observations of smaller black holes. However, this is an imperfect way of doing it, because such light is no longer emitted by the gasses once the cross the event horizon of the black hole. (Which is why astronomers will sometimes refer to black holes as "shining poorly.")

The best way to determine the mass of a black hole is to directly measure the gravitational effect the black hole has on the objects around it. Through careful observation, it's just a matter of plugging the numbers into the well known gravitational equations of relativity. Unfortunately, the only instrument sensitive enough for that is the Hubble Space Telescope, and there are limits to how much time researchers are able to use it to observe what they want.

In a blog post about this discovery, lead researcher Julie Hlavacek-Larrondo remembered that there was a third way to estimate the mass of a black hole, which could be done using the Chandra X-ray telescope. She recalled from previous reading that all non-quasar black holes have "a simple relation between the amount of X-ray and radio waves a black hole emits, and its mass." So the research team turned the Chandra telescope towards known black holes. And that's what led to the astonishing results.

"The masses we obtained from the standard relations systematically underestimated the black hole masses compared to where they should lie on the fundamental plane of black hole activity," wrote Hlavacek-Larrondo. "If our black holes truly follow this fundamental plane, as they should because they 'shine poorly' (unless they are somehow special), then the true black hole masses would be about 10 times higher!"

The next step, though, is to prove the mass of the black hole through direct observation with the Hubble Space Telescope. Hlavacek-Larrondo hopes to get time on the Hubble Space telescope to observe them - and thinks that those observations may yield even larger black holes.

"For some of our objects, I only have lower limits of the mass, which means that the black hole mass could be even higher," she wrote. "I wouldn't be surprised if I end up finding a 100 billion solar mass black hole (the biggest black hole yet discovered is around 30 billion times the mass of the sun)!"